1. Field of the Invention
This application relates generally to digital image scaling. More specifically, this application relates to a raw domain image scaling system and method that maintains consistency while having reduced power consumption.
2. Description of Related Art
In a digital image capturing system, it is common that the resolution requirement for still image capture is higher than that of video output. In such a case, a high-resolution camera capable of supporting the resolution requirement of still image capture is often used. When the camera is used in video mode to produce a video output stream, the data is scaled down to suit the resolution of the video output. For example, a particular image sensor with 8 million pixels (megapixels or MP) can give 8 MP still images. For the same image sensor in video mode, a resolution of 1080×1920 pixels, or approximately 2 MP, may suffice to produce 1080p high-definition (HD) video. Therefore, in 1080p video mode, the image data is scaled down 3× both vertically and horizontally to provide the desired output resolution.
This scaling may be performed either in the raw domain or the RGB domain. An advantage of scaling the image data in the raw domain to the desired video resolution is that it reduces the number of pixels that must be processed through the system. As a result, a majority of processing blocks in an image pipeline or post-processing section can be operated at a lower clock rate than the clock rate required to support full-resolution processing. Operating the processing section at a lower clock rate has significant advantages in reducing electromagnetic interference and reducing power consumption of the system. These advantages are especially valuable in such applications as mobile imaging.
However, existing methods of scaling in the raw domain suffer from several disadvantages, including difficulty in maintaining a Bayer output pattern without resorting to increasingly complex, expensive, and resource-intensive logic circuitry. Additionally, such existing scaling methods suffer from inferior image quality when compared to scaling in the RGB domain. Moreover, to the extent that existing scaling methods rely on such complex, expensive, and resource-intensive logic circuitry, such methods consume prohibitive amounts of power.
Accordingly, there is a need for raw image scaling that can efficiently produce output images of high image quality (that is, with good resolution) which are free of the image artifacts produced by existing raw image scaling, and which are effective without consuming an undue amount of power.